Primary Nasolacrimal Duct Obstruction Visualized on ¹²³I Preablation Scan for Papillary Thyroid Carcinoma

DISCUSSION

Tears drain from the eyes medially via superior and inferior lacrimal canaliculi into the lacrimal sac. The lacrimal sac is seated within an osseous groove formed at the junction of the lacrimal bone and the frontal process of the maxilla. The lacrimal sac is contiguous inferiorly with the nasolacrimal duct. It functions as a reservoir for excess tears that are relayed through multiple mucous membrane folds of the nasolacrimal duct (many with eponymous names) into the inferior meatus of the nasal cavity. Nasolacrimal duct obstruction may result in epiphora or blurred vision. The incidence of nasolacrimal duct obstruction after radioiodine ablation is reported to range from 2.2% to 18% (2), but this may be an overestimation since cases without pretherapy imaging may actually be examples of primary nasolacrimal duct obstruction. Nasolacrimal duct obstruction secondary to radioiodine ablation is more likely to occur bilaterally within 6–18 mo after treatment with doses of greater than 5,550 MBq (3). The transmembrane cotransporter of sodium and iodide (sodium-iodide symporter) highly expressed by the follicular cells of the thyroid is also responsible for radioiodine secretion into the nasolacrimal drainage system, leading to localized radiotoxicity with potential for secondary nasolacrimal duct obstruction (4). Defining the etiology of nasolacrimal duct obstruction has prognostic implications, because external or endoscopic dacryocystorhinostomy (the formation of an anastomosis between the lacrimal sac and the nasal mucosa to bypass the nasolacrimal duct obstruction) is more likely to succeed in patients with primary nasolacrimal duct obstruction than in those with secondary nasolacrimal duct obstruction due to radioiodine ablation or radiotherapy (5). This case demonstrates an additional benefit of pretherapy radioiodine imaging before radioiodine ablation of differentiated thyroid cancers.